In a conventional digital TBC, as described in the U.S. Pat. Nos. 3,909,839 and 4,065,787, an input video signal, having a time-base error due to fluctuations in relative speed between tape transport speed and head rotation speed, is digitized and stored in a digital memory in response to a write-in clock pulse train which also includes a time-base error component. The stored digitized video signal is read out in response to a read-out clock pulse train which does not include the time-base error component. In such a conventional digital TBC, the maximum tolerable frequency range, in which the frequency of the write-in clock pulse train can follow the time-base fluctuation in the input video signal, is such that the phase difference between a color subcarrier in the input video signal and the write-in clock pulse for one horizontal scanning period (1H), corresponds to a period equal to one cycle period of the color subcarrier. When the sensitivity of a voltage sensor, provided in a phase locked loop for generating the write-in clock pulse, phase-locked to the subcarrier contained in the input video signal, is lowered to widen the frequency range, more than one stabilized point in the phase locked loop results. This result makes it impossible to achieve writing in of the digitized video signal in the proper sequence.
It is therefore an object of the present invention to provide a digital time-base corrector in which the write-in clock pulse generated by the phase locked loop can follow greater time-base fluctuations in the input video signal.